Heating at different points in processes for preparing solid foodstuffs, such as cheese-like products and the like, using soybean protein is known to cause certain problems. For example, Japanese Patent Application No. 6107/1974 describes a method for producing processed, cheese-like foodstuffs by kneading a mixture mainly composed of soybean protein isolate having a low gelation ability, casein(preferably a water-soluble casein) and oils and/or fats while adding water to the mixture, sealing the kneaded mixture in a casing, and then heating to cause gelation. In this method, it is important that the kneading is performed without heating. The gel of soybean protein formed by heating is destroyed by the mechanical agitation required for kneading and makes it impossible to form a continuous phase of tight protein. Consequently, the tissue of the resulting product becomes sandy and is not suitable for a cheese-like foodstuff.
Japanese Patent Application No. 146237/1983 describes a method for producing cheese-like foodstuffs by kneading protein mainly composed of vegetable protein (preferably soy protein isolate) with oils and fats and water and allowing the mixture to stand at a temperature of 0.degree. to 60.degree. C. for twenty minutes or longer to cause gelation. This application discloses that heating the kneaded mixture causes the resulting product to exhibit poor melting feeling to the tongue and to have a texture which is dry and crumbling and lacks smoothness.
Japanese Patent Application No. 108333/1986 discloses that good solid foodstuffs can be obtained only by mixing the raw materials in a specific order, namely, adding phosphates and/or citrates (and table salt if necessary) to water, dissolving the mixture, heating the resulting solution, adding protein, edible oils and fats and organic acids in that order and then agitating the mixture.
The methods described in Japanese Patent Application Nos. 6107/1974 and 146327/1983 do not employ mixing while the casein is melting from being heated like in conventional methods for producing processed cheese and, therefore, do not best utilize advantageous physical properties of casein. Also, these methods seriously restrict the use of rennet-casein which has the most excellent flavor among the caseins. Furthermore, the method disclosed in Japanese Patent Application No. 146237/1983 does not include heating the kneaded mixture to a temperature of 60.degree. C. or higher after kneading which results in the product having poor storage characteristics.
The method disclosed in Japanese Patent Application No. 108333/1986 is complicated because the raw materials are added and mixed in multiple stages. This method also requires relatively high shearing forces (high speed agitation) at the stage where the protein is added. If such agitation is performed over a short time period with a low shearing force, there is a tendency to form undissolved lumps which adversely affect the texture of the product.